1. Field of the Invention
This invention relates to color filter arrays and color imaging devices. More particularly, it relates to solid-state photosensitive devices that have a planar array of charge-handling semiconductive photosensors in micro-registration in at least one dimension with a multi-color planar array of filter elements, and to methods for making them. The solid-state color imaging devices are particularly useful for solid-state video cameras.
2. Description Relative to the Prior Art
A reliable, yet sensitive all solid-state video camera would find abundant utility, including use in television cameras, card readers, facsimile recorders, picturephones, character recognition, etc. Solid-state video cameras would be desirable because, in addition to the problems inherent in traditional video cameras of drift, misalignment and short tube life, such traditional, i.e., non-solid-state, video cameras suffer from the complications of registering separate electron beams and the effects of electron beam lag. A relatively simple, efficient solid-state color camera which would overcome these problems is still sought.
Color photosensitive devices using charge-handling solid-state image sensors of various types, for example, charge-coupled devices, known as CCDs, and charge-coupled imagers, known as CCIs, have been proposed and used in video cameras. To avoid optical complexity and problems with image registration, it is highly desirable that color image sensing occur at a single imaging site, e.g., at a single planar photosensitivity array. Many problems are encountered with such "single-site" color imaging, however, because at least three distinct types of color information must be extracted in order to represent a color image in video signal form.
Some of the problems associated with "single-site" color imaging processes are overcome by the approach taken in U.S. Pat. No. 3,971,065, issued July 20, 1976 in the name of B. E. Bayer. In the Bayer approach, color imaging is effected by a single imaging array composed of a large number of individual luminance and chrominance sensing elements that are distributed according to type (sensitivity) in repeating interlaid patterns, wherein the luminance pattern exhibits the highest frequency of occurrence--and therefore the highest frequency of image sampling--irrespective of direction across the array.
To produce an element array according to the Bayer approach or other similar approaches, a solid-state sensor array wherein each sensor has a broad wavelength sensitivity is provided with a superposed color filter array. Methods for providing filter arrays for various purposes are known in the art; however, many of these methods are not adaptable for producing color filter arrays which are useful with a solid-state photosensor array. For example, multilayer color filter arrays that resort to the use of multiple layers are not desirable for single-site color imaging devices, because such arrays require the imaging optics to have a large depth of field so that all layers, as well as the photosensor, are in focus. Further, multilayer arrays can result in misalignment between the individual filter elements and the underlying photosensors.
The present invention provides a method for making a color filter array, preferably having a single layer, using a heat-transfer process to diffuse dyes into a receiving layer capable of receiving dyes. The present invention is an improvement over the heat-transfer process of my coworkers Brault, Light and Martin, described in their commonly assigned, copending application Ser. No. 758,231, filed Jan. 10, 1977, now abandoned, entitled "A Method for Making a Solid-State Color Imaging Device Having an Integral Color Filter and the Device". While their invention provides a simple and effective method for providing color filter arrays for the array of charge-handling semiconductive photosensors, further impovements were sought. More specifically, further improvements in the edge sharpness of the dye deposits are desirable.